Current Analytical Chemistry - Volume 13, Issue 5, 2017

Background: The goal of this research is to develop a new electroanalytical procedure for the simultaneous electrochemical detection of vitamin K1 (VK1) and vitamin D3 (VD3), in a sodium dodecyl sulfate (SDS) -containing buffer solution, with no detectable interference of other kinds of vitamin A and vitamin E present in the sample solution. Surfactant solutions are well known their capability to dissolve oil-soluble substance such as dyes, hydrocarbons, esters, perfumes, and so on. Micellar solubilization is the powerful alternative for the dissolution of poorly soluble or hydrophobic compounds in aqueous environments. Surfactants micellar media can be successfully applied for the solubilization of lipophilic organic compounds in water media and enhancement of their electrochemical activity. In this research, the anionic surfactant SDS was used as the solubilizing agent. Method: Poly (Alizarin red S)/multi-walled carbon nanotubes (poly(ARS)/MWCNTs) film was fabricated on glassy carbon electrode and the modified electrode was employed for the simultaneous determination of VK1 and VD3. The peak-to-peak separation for VK1 and VD3 was about 1.0 V in the presence of SDS in 1.5 M ammonium acetate solution (pH 7.0). In this study, the anionic surfactant SDS was used as the solubilizing agent. The peak intensities for the oxidation of VK1 and VD3 increased at poly(ARS)/MWCNTs functionalized electrode and the modified electrode was used for the simultaneous determination of VK1 and VD3. Results: The poly (ARS)/ MWCNTs film on the bare glassy carbon electrode surface was generated by the electrochemical way and then used for the simultaneous quantification of VK1 and VD3 by employing voltammetric techniques. The peak intensity of VK1 was linear with the concentration of VK1 from 0.5 to 80 μM in the presence of 80 μM VD3 and the limit of detection of VK1 was calculated to be 0.06 μM in the presence of VD3. Meanwhile, the peak intensity of VD3 was linear with the concentration of VD3 from 8 to 160 μM with a detection limit of 5 μM in the presence of 10 μM VK1. On the other hand, vitamins A and E did not interfere with the square wave voltammetry response. Conclusion: The suggested method has been successfully implemented for the simultaneous determination of VK1 and VD3 in plant and in milk samples with good precision and accuracy. The constructed poly (ARS)/MWCNTs functionalized electrode showed a simple and multitalented protocol which ensures an effective detection range, low limit of detection, and good potential implementation towards the simultaneous quantification of VK1 and VD3. Adequate recoveries with admissible errors were achieved for the quantification of spiked standard VK1 and VD3 samples in food extracts. Therefore, the developed procedure can be effectively used for the assay of VK1 and VD3 content in real food samples. Further, this procedure could be an alternative method for the simultaneous analysis of VK1 and VD3 in the future with its adequate sensitivity, stability, good reproducibility and it being devoid of matrix interference.

The microfluidics-based electrochemical biosensor (MBEB) is a new approach to laboratory diagnostics that offers many advantages over the conventional bulky and expensive laboratory instruments. Despite its small size and portability, the biosensor requires a specific sample volume to completely cover the detection zone and be analyzed. However, the sample volume for a particular microchannel size is of crucial importance, and the use of an inadequate sample volume results in less accurate measurements, lower sensitivity and increased detection limits. Therefore, this paper investigated the effects of microchannel size on sensor performance. First, microchannels ranging in size from 100- 1000 μm were fabricated, integrated and bonded to an electrode chip. Cyclic voltammetry scans for four different microchannel sizes fabricated for an electrode size of 100 μm were then conducted. The response and sensitivity of the fabricated biosensor increased with increasing microchannel size. The highest sensor sensitivity was observed using a microchannel size of 400 μm, and the response was maximized when a sufficient amount of the target was loaded in the microchannel. However, further increasing the microchannel size decreased the response current of the sensor due to the uncompensated solution resistance, which was considered a minor factor affecting the sensitivity of the sensor. Thus, optimizing the size of the channel is critical for maximizing the sensor performance.

Background: Metal nanoparticles have important applications in the field of electrochemical (bio)sensors by facilitating or amplifying the electronic transfer between electrode and target biologic compound, or acting as catalysts of electrochemical reactions. Silver nanoparticles are attracting great attention due to their (electro)catalytic properties, and subsequently their potential application in microelectronics, sensing devices and catalysis. The challenge of the silver nanoparticles synthesis consist in obtaining stable and small size nanoparticles, preventing unwanted agglomeration of the colloids and by using various natural polymers. Methods: In the preparation of silver nanoparticles, silver nitrate was taken as the metal precursor and sodium lignosulfonate was used as a reducing/stabilizing agent, considering that lignin derivatives are capable of complexing with silver cations and to reduce them to atomic silver. Cyclic voltammetry, differential pulse anodic stripping voltammetry and UV-vis spectrophotometry techniques have been involved in the evaluation of electrochemical and optical properties of silver nanoparticles. Results: The present work investigates the electrochemical aspects correlated with spectrophotochemical ones of silver nanoparticles prepared by a simple one step procedure and define their catalytic properties. The preparation of silver nanoparticles by a chemical reduction process via lignosulfonate was optimized in respect to their voltammetric behavior revealing the electrochemical characteristics of different silver nanoparticles. The resulting nanoparticles were characterized by means of cyclic voltammetry technique, in two forms: in bulk solution and immobilized as a layer on the electrode surface. The silver nanoparticles- lignosulfonate composites were found to exhibit efficient electrocatalytic activity toward the oxidation of p-nitrophenol. The response of the developed sensor to p-nitrophenol addition is assessed using faradaic peaks current measurements in cyclic voltammetry and differential pulse voltammetry techniques. Conclusion: The electrochemical and spectrophotometric evaluation of silver nanoparticles formation from silver salt and lignosulfonate, without using any other reducing or stabilizing agent and investigating both the effect of silver salt and lignosulfonate concentration. The lignosulfonate polymer demonstrated to be a good matrix for immobilization of silver nanoparticles onto screen-printed electrode and the resulting modified electrode exhibits efficient electrocatalytic activities toward the oxidation of p-nitrophenol.

Background: Rivaroxaban is clinically indicated for the prophylaxis and treatment of thromboembolic diseases. A stability-indicating micellar electrokinetic capillary chromatography (MEKC) method was validated for the analysis of rivaroxaban (RIV), using linezolid as an internal standard (IS), showing the capability to resolve from its potential impurities and degradation products, which is highly recommended for the quantitative analysis of pharmaceutical formulations. Methods: The background electrolyte solution consisted of 75 mM MES buffer and 25 mM sodium dodecyl sulphate (SDS) solution at pH 2. Injections were carried out using a pressure mode at 50 mbar for 60 s, with detection by a photodiode array detector set at 202 nm. Results: Specificity and stability-indicating capability of the method were established in degradation studies, which also showed that there was no interference of the excipients. The method was linear over the concentration range of 0.5 – 50 μg mL-1 (r2 = 0.9991) and the detection limit (DL) and quantitation limit (QL) were 0.16 μg mL-1 and 0.54 μg mL-1, respectively. The accuracy was 100.67% with bias lower than 1.60%. Conclusion: The proposed method was applied to the quantitative analysis of RIV in tablet dosage forms and the results were correlated to those of the validated reversed-phase liquid chromatography (RP-LC) and the anti-factor Xa assay, with non-significant differences (p > 0.05), contributing to evaluate an alternative to improve quality control, and to assure therapeutic efficacy of the pharmaceutical product.

Background: The article describes how a new robust HPTLC method was developed to separate and quantify aspirin, clopidogrel bisulphate and rosuvastatin calcium in a fixed dose combination present in a capsule dosage form using quality by the design approach. Methods: A central composite experimental design has been framed and results were analysed by using a modern statistical technique called response surface methodology in order to study the effects of chromatographic chamber saturation time, volumes of ionic modifier and mobile phase ratio on Rf value and band shape. Results: The Rf value predicted for aspirin, clopidogrel bisulphate and rosuvastatin calcium was in between 0.3 and 0.84. After optimization, the chromatographic conditions were 20 min saturation time and 7:3:0.2 v/v/v as the ratio of ethyl acetate, chloroform and pH modifier (Glacial Acetic acid) as a mobile phase. The LOD was found 45.2 ng band-1 15.9 ng band-1 and 6.8 ng band-1; and the LOQ was found 150.7 ng band-1 53.05 ng band-1 and 22.7 ng band-1 for AS, CL and RO respectively Conclusion: The optimized HPTLC method was validated according to (ICH) guideline Q2 (R1). The results prove that QbD concept effectively optimizes HPTLC methods with the minimum number of experiments. Developed HPTLC method was successfully applied for commercial samples of aspirin, clopidogrel bisulphate and rosuvastatin calcium in triple combination capsule dosage form.

Background: Volatile organic compounds (VOCs) are emitted from a variety of industrial sources and human exhaled breath with endogenous and exogenous origins. For environmental, health, and scientific studies, these compounds must be monitored at trace levels in airborne, gaseous samples and human breath exhales. This article presents the challenges for developing a simple, rapid, non expensive and adsorbent free method for the isolation and enrichment of volatile organic compounds (VOCs) from gaseous samples on the basis of co-liquefaction of analytes and solvent molecules. Methods: A 500 mL spherical glass device was filled with an air sample or human breath exhaled. 0.5 mL of acetone was introduced and exposed to ultra sonification for cold vaporization and then cooled down at -10ºC for co-liquefaction of acetone accompanying with VOCs. Parameters affecting performance of the extraction method were investigated using a mixture of benzene, toluene, ethyl-benzene and xylenes (BTEX) as the model VOCs. For quantitative investigation, 2 μL of the extract was subject to GC-FID analysis. Results: Under optimal conditions, the method displayed good linearity for BTEX within a range of 0.3-800 ng mL-1, with correlation coefficients >0.996. The limits of detection (LODs) and the limits of quantitation (LOQs) ranged from 0.13 to 0.25 ng mL-1 and 0.3 to 0.85 ng mL-1, respectively. The relative standard deviations (n=3) were less than 4.53%. Moreover, enrichment factors (EFs) and extraction recoveries (ERs) were in the ranges of 1075 to 1296-fold and 86-103%, respectively. The overall time for sampling and extraction is 20 min. Conclusion: A novel enrichment method was provided for extraction of volatile analytes from gaseous samples prior to their gas chromatographic analysis. The method is applicable to analyze samples of environmental and/or toxicological interests.

Background: Antifouling paints are widely used for the prevention of growth and development of fouling organisms (biofouling). Consequently, nowadays they are one of the main sources of marine pollution. Objective: The present study examines and compares two different extraction techniques, for the determination of diuron and irgarol 1051 in shellfish tissues. Method: Microwave assisted extraction and ultrasound extraction, followed by liquid chromatography with tandem mass spectrometry were tested and different parameters for both extraction methods were optimized. Results: The results showed that microwave assisted extraction was the most effective method, presenting recoveries in the range of 51.2 to 69.4% and 76.0 to 92.8% for diuron and irgarol 1051, respectively. The precision was evaluated in terms of repeatability for different concentration levels (50, and 500 ng·g-1 of both analytes), which was lower than 19.1% (n = 6) in all cases. The applicability of the proposed method was evaluated by the extraction and determination of the target analytes in different mollusc species collected from Spain and Brazil beaches. Conclusion: The proposed method provides good results in terms of sensitivity, extraction efficiencies and precision and it could be employed for future monitoring studies in ecosystems influenced by the port traffic.

Background: Graphene is easy to aggregate by π-π and Van der Waals interaction between nanosheets, which diminishes the accessible area and limits its real applications in electrochemisty. The construction of three-dimensional graphene and its related nanocomposite is an effective path to overcome this problem. Objective: The aim of this paper is to study the direct electrochemistry of myoglobin on threedimensional graphene-nickel oxide modified electrode and its electrocatalytic detection of trichloroacetic acid. Method: Electrodeposition approach is used to synthesize three-dimensional graphene-nickel oxide nanocomposite. Scanning electron microscopy is used to characterize the morphology of the materials. Electrochemical impedance spectroscopy and cyclic voltammetry are carried out to investigate the electrode performance. Electrocatalysis of myoglobin modified electrode for trichloroacetic acid are conducted by cyclic voltammetry. Results: A three-dimensional graphene/nickel oxide nanostructure is synthesized by electrodeposition directly on carbon ionic liquid working electrode. Direct electrochemistry of myoglobin on threedimensional graphene-nickel oxide modified electrode is successfully achieved with a pair of enhanced redox peaks. The electrocatalytic detection of trichloroacetic acid is established with a wider linear range (0.5~32.0 mmol L-1) and a lower limit of detection (0.16 mmol L-1). Conclusion: This electrochemical trichloroacetic acid biosensor exhibits properties such as high sensitivity and good reproducibility with better stability, which indicates that the three-dimensional graphene/ nickel oxide nanocomposite plays a positive role in the field of third-generation electrochemical enzyme sensor construction.

Background: Duloxetine, which is used to treat major depressive disorder and diabetic peripheral neuropathic pain, can be analyzed with different analytical methods, including high performance liquid chromatography-tandem mass spectrometry, electrophoresis with fluorescence detection, HPLC with fluorescence detection and so on. However, these methods need time consuming sample preparations or special and expensive instruments. It is nessecary to develop a simple, rapid, sensitive and cost effective method for the determination of duloxetine in biological fluids. Methods: A combination of magnetic dispersive solid-phase extraction procedure with high performance liquid chromatographic-ultraviolet detection (HPLC-UV) was developed for the determination of duloxetine in human plasma and urine samples. Magnetic Fe3O4 nanoparticles grafted oxidized-multiwalled carbon nanotube (MNPs-MWCNTs) was used as an efficient adsorbent during the preconcentration step. Results: Under the optimized conditions, the calibration curve was linear over the concentration range of 10-2500 ng mL-1 (R2 = 0.9991). Validation experiments revealed that the optimized method has high percent recovery (96%), high enrichment factor (120), good precision as RSD% (intra-day: 3.28, 3.44; inter-day: 4.29, 4.51 for urine and plasma, respectively, C=1000 ng mL-1, n=6) and low detection limit (2.1 ng mL-1). Conclusion: Obtained results indicated that the proposed method has advantages of convenience, good sensitivity and high efficiency, and it was feasible for the determination of duloxetine in biological fluids.

Background: Cancer medically, is a group of wide range of several diseases which are related with uncontrolled growth process of cells. A cross-sectional study was carried out to assess the concentration of cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) in blood serum samples of cancer patients in comparison with healthy/control subjects. Methods: A total of sixty subjects (30 cancer patients and 30 healthy subjects) were selected for this study from different hospitals of Karachi, Pakistan. Whole blood samples collected, digested and analyzed through graphite furnace atomic absorption spectrometry (GFAAS) for elemental analysis. Results: The results showed that the concentrations of these metals in blood serum of cancer patients were higher than healthy subjects. The mean concentration of Cd, Cu, Pb and Zn were 2.12, 1237.03, 1.87, 1084.74 μg/L respectively. The statistical data obtained was correlated to find the possible interaction between different metals. A negative correlation was observed between Pb/Zn (r = -0.521) in cancer and Cu/Zn (r= -0.431) in healthy individuals. Conclusion: The trend of metals in blood samples of cancer’s patients are as follows: Cu > Zn > Pb > Cd and in healthy individuals are: Zn > Cu > Pb > Cd. The statistical data reveals that there are significant differences found in between healthy and cancers individuals. Regular monitoring study should be carried out to create awareness on metal toxicity.

Background: Cosmetic products are required to be safe for consumers under customary conditions of use. Preservatives are used in cosmetics at relatively low concentrations to destroy, block, and prevent the action of any harmful organisms by biological and chemical means. The frequency of allergy to human skin for most preservatives has been described. For quality control of cosmetic products, the determination of these preservatives is essential. Methods: A simple, rapid and sensitive high-performance liquid chromatography (HPLC) method was developed and validated for the simultaneous determination of preservatives; methylisothiazolinone (MI), salicylic acid (SA), methylparaben (MP), ethylparaben (EP) and propylparaben (PP) in selected cosmetic products. Each compound, together with caffeine (CA) (internal standard) was extracted from the cosmetic matrices with 50% methanol using an ultrasonicator. Chromatography resolution of the preservatives was performed on a Chromolith Speed Rod monolithic silica column (100 mm x 4.6 mm i.d.) with acetonitrile, and 10 mM phosphate buffer (pH 3.0) as the mobile phase under gradient elution conditions. The detection of all compounds was monitored with diode array detection and conducted at ambient temperature. Results: All preservatives were baseline separated at short run-time (< 8.0 min). The proposed method was validated over the range of 0.3–75 μg mL-1 for MI and 0.1–50 μg mL-1 for SA, MP, EP, PP, respectively, and no correlation coefficients lower than 0.999. The recoveries at the concentrations studied ranged from 95.6% to 103.9% with RSDs less than 3.8%. The proposed method was validated in compliance with ICH guidelines, in terms of accuracy, precision, limits of detection and quantitation and other aspects of analytical validation. Conclusion: The proposed method is a powerful alternative approach for identifying and determining of the studied preservatives in commercial cosmetic samples. The limits of detection (LODs) and quantitation (LOQs) at the nanogram level were far below the established restrictions in the Saudi Food and Drug Authority Regulation, demonstrating the suitability of the proposed method for routine control. Simple sample pretreatment with monolithic HPLC-PDA developed method produced a selective and accurate analysis without an LC-MS/MS instrument.

Background: Cannabis is the most widely used illicit drug in the United States and Europe. In recent years, a range of new substances with cannabis-like effects-known as synthetic cannabinoids (SCs) have become popular as drugs of abuse. The use of synthetic cannabinoids and related products has been related to adverse effects including high blood pressure, breathing trouble, hallucinations, paranoia, tachycardia and acute kidney injury. Methods: A rapid, specific, sensitive and validated high-performance liquid chromatography (HPLC) method was developed for the determination of 5F-PB-22 in mouse plasma, for the first time, with its application to pharmacokinetic study. Chromatographies separation of 5F-PB-22 and crizotinib (IS) was performed on Water Symmetry C18 analytical column (100 Å, 150 mm x 3.9 mm, 5 μm) maintained at ambient temperature. The mobile phase consisted of acetonitrile: 0.1% triethylamine (pH 7.0) (60:40, v/v) pumped at a flow rate of 1.0 ml min-1 with run time of 6 min. The analytes were detected at 230 nm. 5F-PB-22 and the IS were extracted from mouse plasma using the deproteinisation procedure, followed by injection of an aliquot of the supernatant into the chromatography system. Results: The results showed a linear calibration curve in the range of 5-1000 ng mL-1 (r2 = 0.9996) with a lower limit of detection (LOD) of 1.5 ng mL-1 in plasma. Precision and accuracy analysis showed acceptable coefficients of variation and relative error, fulfilling the criteria normally accepted in bioanalytical method validation. Conclusion: The proposed method proved to be suitable for screening of 5F-PB-22 in plasma samples, proving to be sensitive and presenting appropriate selectivity and sensitivity, allowing detection of a nano-concentration range of the analyte. The assay was successfully applied in a pharmacokinetic study.